Lloyd Lamble, who has died aged 94, was one of the ever-present supporting actors of British cinema during its monochrome era, best recalled as Joyce Grenfell's fiance in the St Trinian's series. Despite often portraying authoritarian English figures, in real life he was Australian, and had left that country after being suspected of communist sympathies.

Born in Melbourne to a family of musicians, Lamble attended Wesley college, where he sang in the choir. He had already worked on radio before making his stage debut in 1934. Touring the country and New Zealand, his work included singing and stooging for comedians, as well as straight plays.

Aghast at the low salaries for actors, Lamble was president for six years of what was then called Actors' and Announcers' Equity. His own radio work had included government propaganda during the second world war. In 1949 Australia's Commonwealth Investigation Service claimed, inaccurately, that he was "a definite communist". Stage and radio work dried up and, after a stint as a salesman, he fled to London, on a forged passport, in 1950.

Lamble had a receding hairline, a deep voice and an air of solidity which proved well-suited to trench-coated inspectors, court officials and military men. And the then thriving British film industry found him appropriately reliable in real life. His understated manner contrasted with the theatrical style of some of his co-stars, especially in comedy.

One of his first films was Curtain Up (1952), starring Robert Morley. Others included Alfred Hitchcock's The Man Who Knew Too Much (1956), Our Man in Havana (1959) and The Trials of Oscar Wilde (1960). Having already worked for Frank Launder and Sidney Gilliat in The Story of Gilbert and Sullivan (1953), the pair then cast Lamble in The Belles of St Trinian's (1954), as the "silly old superintendent" fiance of Grenfell, the enthusiastic WPC Ruby Gates. He returned for Blue Murder at St Trinian's (1957) and The Pure Hell of St Trinian's (1960). Despite nearly losing her to Terry-Thomas in the first sequel, he was always putting off Gates's marriage plans, causing her to complain, "you used to call me your little blue lamp baby".

Lamble's television debut was in The Passing Show (1951), a series of musical biographies, followed by a live Sunday night play, No Smoking! (1952). His big screen experience was invaluable for early filmed ITV series such as Douglas Fairbanks Presents, William Tell and the short-lived Errol Flynn Theatre. Other guest appearances extended from the prosaic and unintentionally hilarious Fabian of the Yard (1955) to the polished surrealism of The Avengers (1965), as a vanished scientist, and The Prisoner (1967), as a ministry man.

More important roles came in two Armchair Theatre segments in 1960, Clive Exton's Where I Live (1960), as the favoured son of an ailing father, and The Stranger, by Angus Wilson. The Outstation (BBC2, 1968) was a tropical tale, adapted from Somerset Maugham by Simon Raven. Unfortunately for Lamble, he was a regular on the motel soap Crossroads in its early years; fortunately for his reputation and for posterity, none of his episodes are known to exist.

One of Lamble's most frequently screened appearances was early on in Philip Mackie's The Naked Civil Servant (1975). As Quentin Crisp's staid father, he demands of John Hurt's Crisp: "Do you intend to spend your whole life admiring yourself?" And receives the unforgettable reply: "If I possibly can."

Returning to the theatre in the early 1970s, Lamble had a successful season in Dundee, and was later seen in plays as varied as Macbeth and Alan Bleasdale's bawdy satire Having a Ball. The 1980s West End revival of Me and My Girl, with script additions by Stephen Fry, was one of Lamble's last engagements before retiring. In 1996 he donated an unpublished autobiography, dealing with his Australian career and displaying some of the insecurity common in the profession, to the National Library of Australia.

He was married three times, the third time to fellow actor Leslie Jackson, who came with him to Britain. She survives him along with a son and daughter, an adopted son and daughter and three grandchildren.